The Ghost of the Moby Dick
by DarkStarlet
Summary: Ace has gone up against Teach, their battle nearly destroying a whole island, but at the last moment, instead of being captured and sent to his death, Ace is saved by an old friend. This friend loses control of their Devil Fruit power and ends up becoming a ghost on the Moby Dick. Will they ever regain their body again? AceXOC Rated M for Mature content
1. Introduction: Burning Flight

**The Ghost of the Moby Dick**

 **A One Piece Fan-fiction**

 **Disclaimer: I do not own One Piece or any of its characters, only my OC and the plot.**

 **Introduction: Burning Flight**

Fire and shadow engulfed the island.

Fire Fist Ace lay defeated by Marshall D. Teach.

As the traitorous figure approached the prone body, intent on capturing him, a purplish flicker of energy hovered above Ace protectively. It flashed into human form, a young woman with shoulder length, dark brown hair, and venom in her hazel eyes. It was all Teach got the opportunity to see before she grabbed his opponent and they both flickered out of existence in a chaotic flash of purple sparks.

He shouted and spat with fury, curses raining from his foul lips like acid rain in a storm.

Marco leaned on the main mast of the Moby Dick, watching the rest of his crew enjoy themselves. It had been a good day so far, nice weather, no blasted marines to deal with. Nothing all that interesting at all really, but sometimes that was for the best.

A cry went up in the crows nest, a strange fiery ball of light was flashing through the sky. It was there one moment, and gone the next in a cascade of sparks.

It hurled towards the deck, and vanished just before striking the sails, reappearing about a foot over the boards before solidifying into two figures who thudded into the hard wood.

Marco rushed over, ready to attack if need be, but recognised Ace, his friend and crewmate. The woman he did not know, but it seemed that whatever strange power she had, she'd used it to bring Ace back, battered and bruised as he was.

She stirred and slowly stood up, wobbling slightly. Those of the crew who had previously been members of the Spade Pirates called out to her.

"Cass!?"

"How did you find us Cassie?!"

She looked around and spotted Marco frowning at her intently. She raised her palms in a sign of surrender and smiled.

"Woah now, I am friend, not foe. Ace got into a bit of an argument with an old crewmate of yours, Teach. He's a bit banged up but he'll be okay-"

She flinched as sharp purple sparks flitted over her form and she seemed to flicker in and out of view for a moment, her expression one of pain.

"Shit... Think I might have overdone things... I've never moved that far before, even by myself it'd be a strain."

Marco watched as she knelt down to check on Ace, and as his eyes opened, the Phoenix of the Whitebeard Pirates, dashed to his side to help him sit up.

Ace blinked in confusion, wondering what had happened, and where he was.

"Hey Marco, how's it goin'?" He mumbled in a daze before spotting Cassie also leaning over him, "Oh? Cassie? When'd you get here? Finally decide to join us?"

"Not for long by the looks of things." She grimaced as her form wavered once more, "Looks like this is goodbye Ace."

She slumped to her knees, wrapping her arms around herself as though it would keep her together. Ace sat up straighter, confusion in his eyes.

"What do you mean? Where are you going?!"

Cassie smiled as she flickered in and out of view, a bright joyous smile.

"No! NO!" Ace shouted as she vanished completely from his sight. His hand reached out and passed through the space where she had once been, clutching at nothing.

 **Please note that is is the first draft and is not yet complete. Reviews are most welcome.**


	2. Chapter 1: The Ringing of Bells

**Chapter 1: The Ringing of Bells**

Ace lay in his bunk and stared at the roof of the cabin, glaring at the grain of the wood. Wondering again and again, where Cassie had come from, how she had saved him and what had truly happened to her?

Marco sat with a book at the desk, flicking through it. After learning what he could from the Spade Pirates and Ace, he figured out that Cassie must have eaten the Itō Itō no mi, the Move Move Fruit. It was a Logia type, that gave the user the ability to move objects, people and themselves into any free space. It was an unpredictable power, and every user he'd been able to find in his books had so far died using it.

He looked up at a frustrated sigh from Ace, who then punched his pillow. Before going back to his book.

It was a few hours since Cassie has transported them to the ship, and Ace had refused medical care in favour of stewing in his bunk. He had told Marco of how he had come to meet Cassie, a couple of years ago when the Spades had first entered the Grand Line, and how he had tried jto get her to join his crew. She had accepted, but intended to find a few members of her old crew, the Bladed Pirates, to take back some of her belongings before becoming an official member.

The ex-Spades were also all depressed, moping about the place. Even though they had only spent a few happy days with the woman, they had counted her as a friend and crewmember.

Marco's eyes widened for a moment as he re-read the page before leaping up and grabbing Ace's arm.

"She's alive! Ace! She could still be here, we just can't see her."

They both tore from the room and raced back to the deck where Cassie had vanished earlier.

Marco scanned the page of his book once more and looked about the deck for some sort of sign, Ace doing his best to help him.

There was one case of a Move Move user going through the same experience, they had lost control of their ability, and had spent nearly a week between spaces, able to see and hear, but not affect the world around them. No one had been able to see them, except when they had concentrated and brought themselves back to their physical form. If they could just tell Cassie about this, maybe she would be able to come back?

Whitebeard, Edward Newgate, heard the commotion, and for the second time that day, made his way onto the deck to find Ace looking frantic.

"Cassie! You have to concentrate! You can come back, you just have to concentrate!"

"What is going on?" He asked calmly. Marco handed his captain the book he had been reading, and let him read the passage about the last Move Move user.

The quiet, calm of the evening was broken by Ace's shouting, both he and Marco looking for Cassie's presence.

"Are you even still here? Cassie... give us a sign, please." Ace shouted.

The rest of the crew looked out over the deck, all waiting to see what would happen next.

A bell rang.

There was no wind, and the ship was steady... How...?

The bell rang.

Ace darted over to the bell near the base of the stairs, and watched as a tiny purple spark struck the bell, causing it to ring for a third time.

"She's here! She's still here! Marco, what else does it say?" Ace turned back to his friend excitedly, hope back in his eyes.

The Phoenix flicked quickly through the pages but shook his head.

"Just that the last user was in the 'space between places' and that they 'concentrated hard and through sheer force of will, brought themselves back into being.' It doesn't say anything else."

Ace frowned, "Well that's not much help."

The bell rang.

Cassie understood. In the flickering, shadowy world she was in, she heard Ace's voice.

Though her non-existent body and mind was wracked with pain, she knew what she had to do, but she wasn't sure if she could do it.

Cassie concentrated, she tried to bring herself back into physical form, to become real once more, but it was a lot more difficult than that.

The Whitebeard crew now knew all about how she had met the Spade Pirates. She'd heard them talking at dinner.

~ ** _Flashback_** ~

Ace and the Spade Pirates had been on the Grand Line for a few months, they had visited a few islands, got in plenty of trouble, and enjoyed every minute of it.

A new island came into view before them and they headed towards it excitedly. It was a small summer island, and seemed to be uninhabited. They had it all to themselves.

Or so it seemed until they came across some snares set for catching rabbits.

They followed the trail they'd found back to a small clearing in the forest. There they found a tiny hut that looked to have been there for a couple of years. Outside, napping in the sun, was a woman. She wore a grey and white tank top and dark green short-shorts covered in gold studs, her dark hair splayed out on the grass beneath her.

She woke suddenly, as if sensing their presence, and she vanished instantly in a crackle of purple sparks.

Ace and the Spade Pirates looked all over the island but couldn't seem to find her again, though they were certain she was near due to the occasional crackle of energy that startled them every once in a while.

A little perturbed but not put off the island completely, they slept on the ship where they felt somewhat safer.

Cassie landed silently on the deck of their ship and looked around before finding Ace sleeping in his own room, tangled in the sheets. She sat on the edge of the bed and looked at him for a while, wondering who he was and why he had set out to sea.

Ace opened his eyes to see the strange woman from before perched comfortably on his mattress. His fingertips burst into flame as he reached out for her, but she flickered out of existence only to appear near the door, leaning against the frame.

"Well that's not very nice... I only came to say hello..." She said with a mock pout, "I guess it's been a while since I've had to use my social skills."

"Who are you and what are you doing on my ship?" Ace asked in a low, warning tone, making it clear he didn't like her being here.

"Who are you and what are you doing on MY island?" She retorted in a slightly squeaking imitation of his voice. Cassie smiled and opened the door slowly.

"If you want answers, you'll have to catch me first, boy." She winked and slipped out quickly.

Leaping up Ace grabbed the door before it could finish closing and looked around for the odd girl. She was gone, but the faint crackle in the air told him she was still somewhere on the ship.

Rather than waking the rest of the crew, Ace went looking for her himself. He found her leaning against the ships wheel, but once more she disappeared before he could grab her, leaving only a faint giggle behind.

So it went until morning, when the crew woke to find their exhausted captain sleeping against the base of the main mast and the vanishing woman balanced atop the crows nest.

She came down and explained herself to them, about her devil fruit powers, and how she had secluded herself on this island after leaving her last crew.

When Ace awoke he found them having a barbecue on the beach, laughing together. He leapt onto the sand and joined them, her open, friendly attitude a pleasant change from her sarcastic teasing the night before.

She introduced herself as Cassandra Espina, formally of the Bladed Pirates, and explained how her captain had betrayed her to the marines due to her high bounty. How she had escaped, hunted him down, killed him, and scattered the rest of the crew to the dogs.

The Spade Pirates told her of their adventures, and of their meeting Red-Haired Shanks.

After a couple of days Ace informed Cassie that he and the crew were ready to leave. She seemed disappointed but had known they would leave eventually.

"You know, you could come with us. You could join my crew!" Ace grinned.

Surprised, Cassie wasn't too sure how to respond at first, as this wasn't what she had expected to come from him.

"Wait... You're serious?! I... I dunno. I've never really thought about joining another crew." She looked up into the clear skies with a smile, thinking carefully.

Ace tilted his hat back and followed her gaze for a moment before nudging her with his elbow.

"Hey! Okay okay! I'll join you, but not yet, I've got some stuff I need to sort out first. Some of my old crew have a few things of mine that I need to collect."

Ace laughed with her and slapped her back in good humour before leaping onto the ship.

"I'll see you when I see you, Ace!" She called as she waved back wildly.

"That's Captain Ace to you!"

~ ** _Present Day_** ~

Cassie watched them talk, and drifted back to the main deck where she found Ace and Whitebeard in conversation.

"I'm fine. I need to be here."

"You think staying awake here is going to do your friend any good?"

"She saved my life! I can't just leave her alone!" Ace retorted.

Cassie flicked his hat off his head making it tumble to the floor. She tried to tweak his ear but couldn't quite grasp it.

Ace looked around excitedly once more, and felt something tickle his ear.

"Cassie!?"

She tried again, and flicked him in the forehead, this time making contact, her hand materialising for a moment where both the men could see it.

"Ow!"

"I think she agrees with me!" Newgate laughed, his voice booming across the deck.


	3. Chapter 2 - Heart Stealer

Chapter 2: Heart Stealer

The next few days passed without much progress from Cassie, and she kept getting distracted by the crews antics.

First it was them fighting a Sea King, one that resembled a giant eel, and then it was the partying later on. She watched them laugh and drink, and eat. She listened to them sing and shout, and longed to join them.

Marco saw a few sparks out of the corner of his eye, just off behind him, and turned to see Cassie's form flicker into view for a split second. He walked over to the space and waited to see if she would appear again. When she did not he sighed softly and wondered what would happen to her if she didn't come back. Would they find her body? Or would she really become a ghost?

Whitebeard didn't seem too bothered by the whole situation, and seemed to take things in his stride like he normally did. He was grateful that this strange girl had saved Ace's life, and for that he granted her his tolerance.

Cassie kept trying, but being unable to eat, drink or sleep in that state, was starting to take its toll.

She was weakening.

The following morning, most of the crew had hangovers and were still asleep, and even the watch had passed out. It was exactly what the marines had been waiting for.

After Ace's defeat, they had been expecting delivery of the Fire Fist by Teach's hand. When no such package arrived, they demanded an explanation.

Cass the Witch had apparently returned, and saved Ace, right under Teach's nose.

Tracking the Moby Dick, they had made note that Fire Fist Ace was indeed aboard, but there seemed to be no sign of the woman. Since all was quiet, they decided to see if they could capture any pirates by themselves.

Their captain wanted to prove himself to the world government. If he could bring back Ace, or any other major member of the Whitebeard crew, he'd probably be given a promotion.

They moved in silently at little before dawn, and scaled the sides of the ship unnoticed.

Cassie could only watch as they crept about the ship, she found herself unable to touch anything, to ring a bell or bang a door. She was powerless to stop them.

A roar announced Whitebeard's fury a few moments later, and the marines hurried back to the deck, rallying to their captain.

The Whitebeard crew stormed up and surrounded the marines, who took a stand and pulled out their guns. They fired into the crowd of pirates, wounding some, but not doing any real damage.

A shill scream filled the air, and blood splattered onto the ground from no discernible place.

The seastone tipped bullets had had an effect on Cassie, despite her not actually being in physical form.

The Marines looked around confused, just where had this strange scream come from? But their captain couldn't care less. He took a stand, raising his sword and pointing it right at Whitebeard's head.

"Die pirate scum!" He yelled before moving to attack. He stopped, something strange appearing in his vision. An apparition of a woman reaching out towards him. She seem to be walking closer and closer, a deadly darkness in her eyes.

She vanished, and then reappeared a little closer, the edges of her body fuzzy and flickering.

Cassie wanted to protect the crew, to help them and ensure none of them would be captured. Thus, without really realising it, she had willed herself into a sturdier form in order to attack the marines.

As she neared them, the captain glanced at his men and the opposing pirate crew. Fear was in his men's eyes, and a quiet smugness in those of his enemies. He backed up, bumping into the railing at the edge of the ship, and glanced down as Cassie touched his chest.

Extreme pain lanced through him, and he spasmed before going very still, his fellows confused at first.

As Cassie stepped back, still flickering away, her now blood covered hands dropped something to the deck... The marine captain's heart.

His body tumbled backwards over the edge, splashing into the sea with a fateful finality that sent the rest of them scurrying for cover, leaping back aboard their ship, and otherwise fleeing for their lives.

The Whitebeard pirates roared and jeered, shaking their fists in the air, brandishing weapons.

Cassie couldn't quite keep hold of herself for very much longer, and winced as her body started to vanish from view again.

Suddenly she was cold and wet, Newgate having dumped a bucket of sea water over her head...

And she was still there.

The crew looked a little confused.

"I would have thought this was obvious." He chuckled in his booming voice as he clapped Cassie's shoulder nearly knocking her over. He then turned and watched the marine ship high-tail it away, then signalled to Marco.

The blonde lit up, his blue-white flames dancing across his arms, making wings that propelled him high into the air, and towards those who were fleeing from him. The ship exploded in a massive ball of fire, it was unknown if there would be any survivors.

Shocked, Cassie fell to her knees, eyes wide.


	4. Chapter 3 - Recovery and Initiation

**Chapter 3: Recovery and Initiation**

The moments after the short battle were almost in slow motion for Cassie, she was happy to be back in solid form, but was still wounded by the bullet, she sat for a few moments wondering what to do, stunned still.

Whitebeard called for his doctors to see to her, and a pair dashed over, but not before Ace reached her and pulled her in to a rib crushing hug.

"Ugh, Ace! Bullet wound!"

"Ah, sorry." He smiled, glad she was back.

He accompanied her to the medical bay where she did her best to lay still as she was stitched up.

"How the hell did you find me?" He wondered aloud.

"Wasn't hard, I was keeping tabs on you, and turned out I was in the area when all that shit went down with Teach. It's not like it was hard to see an exploding island, boy."

"I'm glad you were there though... It was getting a little heated in there."

"Understatement of the fucking year Ace." She laughed, "Ow... Damn laughing hurts."

After she was cleared to leave, she walked with Ace to the galley to join the rest of the crew for lunch. They sat together, joined by the other ex-Spades, and chatted together about things that had happened to them since they had last seen each other.

Ace once more fell asleep face first into his plate, and Marco noticed Cassie's head drooping too, her exhaustion catching up to her. As her head finally came to rest on the wooden table, he smirked and walked over, poking Ace roughly on his way past to wake him up.

"Oi, get up, you've got your own bed to sleep in."

Marco carefully picked up the slumbering woman, who didn't even stir she was so out of it, and carried her to Ace's bunk.

The crew then had a few repairs to make due to the Marines and as first mate, he had to oversee them.

Whitebeard called Ace to his private study to talk.

"This woman was a member of your old crew, unofficial or not, you agreed your whole crew would join, that would mean her too. This family just keeps growing."

"Yeah... I dunno how she'll take that though. Her last crew were major assholes."

"So I've heard. You talk to her, and we'll sort it all out later."

"Sure." Ace nodded before leaving to go and find her.

He entered his cabin and saw her completely unconscious in his bed. Sitting down at the tiny desk he decided to wait until she woke up. She deserved some rest after what she'd been through.

She'd refused to talk about what it was like between worlds, and hadn't mentioned what it had felt like either, but he could tell she'd deliberately left out that experience.

Nearly a full day after she'd fallen asleep, Cassie finally awoke to find Ace on the floor beside the bed, snoring softly. She sat up slowly, not wanting to tear her stitches, and swung her legs out, stepping lightly to avoid standing on the pirate. She still felt heavy and slow, and knew it would be a while before she was back to her old self again. Walking softly into the early afternoon sunlight on deck, she was greeted by the crew as though she was one of their own already.

Leaning on the railing and looking out to sea she sighed and closed her eyes, letting the breeze roll over her.

"Ace talked to you yet?"

Not expecting the voice she jumped and turned to find Marco leaning on the railing next to her. He smirked.

"Uh, no... He's still asleep, on the floor."

"Typical Ace."

"Yeah, seemed that way, but family's a big thing for Ace, and your crew is like a family, so I guess it's understandable."

"You're not crew, not yet anyway. Ace was supposed to talk to you about that. Since you were an unofficial member of the Spades, and they joined us, that makes you an unofficial member of the Whitebeards."

"Huh? Hadn't thought of it that way."

"Decision's not up to me though. That's for the Captain to decide. You should probably go see him. As a non-crew member, he's been very giving towards you."

"I suppose I should at least go thank him for that." She laughed, glancing up towards the blonde.

Marco jerked his head towards the door she would need to take to speak with the intimidating hulk of a man, and walked away.

The study door was open, and Cassie knocked on the frame and waited outside the room. When Newgate waved her in, she stepped forward nervously.

"Um..."

She didn't know what to start with.

"I, uh, just wanted to... thank you, for, you know... all the help you've given me. So, uh, thank you sir."

"You saved the life of one of my sons. A debt had to be paid."

"Don't make me any less grateful though sir."

A chuckle escaped the large man.

"Turns out you are supposed to be one of my crew members, but why should I let you join?"

"Oh...? Uh..."

She hadn't been expecting an interview.

"Well... I... I've got pretty cool powers... when they're working right... Um... but..."

"But?"

"But that's not why I should be part of your crew! Ace and the others, they're my friends, and I protect my friends, so even if you don't have me join your crew, I'll still be around. Whether you like it or not!"

Turning bright red with embarrassment she looked down at the floor. What had possessed her to spurt that at the most dangerous man on the sea?!

A loud guffawing laugh burst forth and Newgate slapped his hand down on the desk before rising.

"Looks like you'll fit right in around here! And I get a new daughter! Gwahaha!"

"What? You mean... You've already decided?"

Whitebeard grinned, "Welcome to the crew!"

The afternoon passed into evening, and drink was flowing when Ace finally roused from his slumber. He rejoined his crew on deck and spied the ex-Spades chatting away with Cassie who was sitting awkwardly in a chair.

The familiar buzz of a tattoo gun reached his ears. Realising what was happening he walked over quickly to see the half-finished Whitebeard symbol now decorating the woman's lower back.

"You joined?" He asked with a grin.

"Well I ain't getting this tat for nothing! 'Course I joined. You didn't think I'd bail on you after all the trouble I went through to save your hide?" She laughed back.

Ace sat on the deck and chatted with Cassie until the same mark that adorned his back and shoulders found its place above her hips, before heading to dinner with her.

The crew sat together and toasted a welcome to their new member before tucking in to the feast laid before them.

As things drew to a close, Cassie was shown to a room she could call her own, and she placed her few belongings there.

There were some clothes that went into drawers fitted under the bed, a couple of books added to the single shelf above the head of the bed, carefully strapped in. On the tiny desk she placed a photo frame, a hairbrush and a small makeup bag.

This would be her home now, at least, she hoped it would be.


End file.
